The primary objective of this research is to contribute to the more effective use of nonhuman primates in any experimental program in which it is necessary or desirable to know blood types of the animals involved. To this end we have developed typing serums detecting several factors. Additional antiserums are being tested for specificity. We are continuing to study the ability of certain blood factors to induce mild or severe transfusion reactions and the deviations from normal physiological functions involved in these reactions. Other continuing studies include induction of tolerance to red cells during fetal life, spontaneous or induced erythroblastosis in monkeys, relationship of certain blood factors to a metabolic disease in Celebes apes, and autoimmune hemolytic anemias. We are also studying the effects of massive transfusions of blood into nonimmunized monkeys undergoing surgery with expected long postoperative recovery periods. As a continuation of the tolerance experiments we hope to study the effects of transfusions of maternal blood to the fetus during the last three weeks of fetal development.